<section app-tutorial-content>
<p>
The Controller upgrade gives access to some new structures: walls, ramparts, and extensions.
We’ll discuss walls and ramparts in the next Tutorial section, for now let’s talk about extensions.
</p>
<p>
<b>Extensions</b> are required to build larger creeps. A creep with only one body part of one type works poorly.
Giving it several <code>WORKs</code> will make him work proportionally faster.
</p>
<p>
However, such a creep will be costly and a lone spawn can only contain 300 energy units.
To build creeps costing over 300 energy units you need spawn extensions.
</p>
<div class='tutorial-controls'>
<md:button class='md-raised md-primary' ng:click='Tutorial.next()'>Next</md:button>
</div>
</section>
